It is known to use a torque converter lock-up clutch in a torque converter of an automatic transmission to improve vehicle performance, and particularly engine gas mileage. Early torque converter lock-up clutches were hydraulically controlled by transmission valve bodies. Following the development of computerized engine control systems, torque converter lock-up clutches are now predominantly controlled by a vehicle's electronic control module (ECM).
A torque converter conventionally provides a fluid coupling between an output shaft of an engine and an input shaft of an automatic transmission. The torque converter functions primarily as a torque multiplication device to increase the amount of engine output torque delivered to the automatic transmission. In certain modes of engine operation, torque multiplication is not desirable and serves only to reduce engine performance and fuel economy. Thus, a torque converter lock-up clutch is used to selectively mechanically couple, or lock up, the engine output shaft to the automatic transmission input shaft to eliminate the torque multiplication function of the torque converter and improve engine performance. The lock-up clutch is typically rotatably fixed to the input shaft of the transmission and can be selectively engaged with an impeller drive plate of the torque converter which is rotatably fixed to the engine output shaft. When engaged to the impeller drive plate, the lock-up clutch, and hence the transmission input shaft, is directly mechanically coupled to the engine output shaft and thus rotates therewith to eliminate torque multiplication.
In most instances, a torque converter lock-up clutch is controlled by an electric solenoid which selectively positions a hydraulic fluid shuttle valve in accordance with an actuation signal applied to the solenoid. The shuttle valve operates to regulate hydraulic fluid pressure acting on the lock-up clutch. When hydraulic fluid pressure acting on the lock-up clutch is increased, the lock-up clutch is displaced to disengage from the impeller drive plate and effect torque multiplication. When hydraulic fluid pressure is reduced, the lock-up clutch engages with the impeller drive plate and a direct mechanical connection is established to eliminate torque multiplication.
The electric solenoid of the lock-up clutch is actuatably controlled by a signal generated by an ECM in response to various engine operating conditions. In accordance with an engine control algorithm, the ECM typically monitors various engine operating parameters through sensors such as a throttle position (TP) sensor and a manifold absolute pressure (MAP) sensor to determine whether to actuate or deactuate the lock-up clutch electric solenoid.
With most vehicle transmissions, under certain engine operating conditions, the engagement and disengagement of the lock-up clutch via the ECM can occur frequently with, or without the transmission ever shifting gears, i.e. downshifting or upshifting to a different gear ratio. The frequent engagement and disengagement of the lock-up clutch causes a bothersome effect known as "transmission hunting" whereby the transmission appears to be indecisively shifting between gear ratios in a quest to determine the optimal gear ratio for the given engine operating condition.
In vehicles which incorporate automatic transmissions, it is desirable to delay the actuation and/or deactuation of the torque converter lock-up clutch until the transmission is operating in a 4th or high gear ratio, or at least until the vehicle is operating above a predetermined speed to minimize the effects of actuating and deactuating the lock-up clutch.
FIGS. 5 and 6 illustrate two embodiments of a known aftermarket device 10 which actuates an electric solenoid 12 of a torque converter lock-up clutch (not shown) only when (1) a vehicle is operating above a predetermined speed, or the transmission is in a high gear ratio, and (2) a brake pedal (not shown) is not depressed. A "normally closed" brake switch 16 supplies a 12 VDC source voltage to a first side of the electric solenoid 12 only when the brake pedal is not depressed.
Once the device 10 detects that the transmission has shifted into the high gear ratio, or that the vehicle is operating above the predetermined speed, a switching transistor is forward biased which couples a second side of the electric solenoid to ground. As long as the brake pedal is not depressed, the electric solenoid 12 will remain actuated to cause the lock-up clutch to engage an impeller drive plate (not shown) of the torque converter as previously described. If the brake pedal is depressed while the lock-up clutch is engaged, the brake switch 16 will "open" to deactuate the electric solenoid 12 and reestablish a fluid coupling between the engine and automatic transmission so that the vehicle will decelerate uniformly. Otherwise, a direct mechanical connection between the engine and automatic transmission would cause an undesirable "jerking" sensation during deceleration of the vehicle.
FIG. 5 illustrates one embodiment of the known aftermarket device which includes a PNP switching transistor 18 for actuating and deactuating the electric solenoid 12, and a "normally open" pressure activated contact switch 20 which closes when a predetermined hydraulic fluid pressure level in a hydraulic fluid passageway (not shown) of the transmission 14 is reached. The pressure switch 20 closes only when the vehicle is operating above a predetermined speed, or the transmission is in the high gear ratio.
FIG. 6 illustrates another embodiment of the known aftermarket device which includes an NPN switching transistor 22 for actuating and deactuating the electric solenoid 12, and a "normally closed" pressure activated contact switch 24 which opens when a predetermined hydraulic fluid pressure level in a hydraulic fluid passageway (not shown) of the transmission 14 is reached. The pressure switch 24 opens only when the vehicle is operating above a predetermined speed, or the transmission is in the high gear ratio.
The known aftermarket device 10 is installed by first disconnecting the existing wiring harness connector coupled to a receptacle on the transmission extension housing. Second, a male-type connector end of device 10 is connected to the receptacle on the transmission housing, and a female-type connector end of device 10 connected to the existing wiring harness connector. On most transmissions, either one of the pressure contact switches 20, 24 is installed within the transmission by the manufacturer. However, on transmissions without a pressure switch already provided, a plug can be removed from the transmission housing and an external pressure activated contact switch can be threadably coupled thereto for communication with the high pressure fluid passageway. Further, for transmissions utilizing a "normally closed" pressure activated contact switch as shown in FIG. 6, an external ground lead 26 of device 10 must be connected to a vehicle ground.
One disadvantage of the known aftermarket device 10 is that, once installed, the device 10 disables an electronic control module (ECM) 28 such that the ECM can no longer assert control over the electric solenoid 12 under any circumstances. The ECM is disabled because the ground side of the electric solenoid 12 is controlled by the respective switching transistors 18, 22 in place of a first control line 30 of the ECM when the device 10 is installed.
A vehicle incorporating the known aftermarket device 10 was tested by an EPA certified laboratory for compliance with EPA vehicle exhaust emission requirements. The results of the test indicated that under certain driving conditions, i.e. travelling up a slight incline with a constant throttle position, the aftermarket device 10 failed to release the lock-up clutch so that torque multiplication could be utilized. As a result, the vehicle developed a lean misfire condition wherein NO.sub.x emissions were increased beyond acceptable EPA limits. The failure of the EPA emission test was a direct result of the device 10 circumventing the ECM control over the lock-up clutch because the ECM is typically programmed to release the lock-up clutch under such driving conditions. As a result of the failed EPA test, the California Air Resources Board (CARB) has refused to grant permission for marketing and/or selling the known aftermarket device 10 within the state of California.
Thus, it is an object of the present invention to provide an aftermarket device for permitting an electric solenoid of a torque converter lock-up clutch to be selectively actuated and deactuated by a vehicle electronic control module only when the vehicle is operating above a predetermined speed, or the transmission is in a high gear ratio.
It is also an object of the present invention to provide a device for disabling an electric solenoid of a torque converter lock-up clutch when a vehicle transmission is not operated in a high gear ratio, and for enabling the electric solenoid to be selectively controlled by a vehicle electronic control module only when the vehicle is operating above a predetermined speed, or the transmission is in the high gear ratio.
It is yet another object of the present invention to provide a simple, cost effective, and quick aftermarket solution to the problem of "transmission hunting".
It is a further object of the present invention to provide an aftermarket device which utilizes existing sensors, switches and hydraulic passages to control the operation of a power transistor which permits actuation and deactuation as an electric solenoid of a torque converter lock-up clutch under certain engine operating conditions.
It is a further object of the present invention to provide a non-invasive aftermarket device to solve the problem of "transmission hunting" without the need to modify the transmission or the ECM outputs connected thereto.
It is a further object of the present invention to provide an add-on device which relies solely upon an output signal from a hydraulic pressure contact switch to determine whether to enable or disable an electric solenoid of a torque converter lock-up clutch.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.